diff --git a/common/values/string_value.cc b/common/values/string_value.cc
index b9495fa69..914f6e496 100644
--- a/common/values/string_value.cc
+++ b/common/values/string_value.cc
@@ -667,8 +667,11 @@ absl::StatusOr<std::pair<size_t, size_t>> SubstringImpl(
     ++size_code_points;
     size_code_units += code_units;
   }
-  if (size_code_points == start && start == end) {
-    return std::pair{size_code_units, size_code_units};
+  if (size_code_points == start) {
+    start_code_units = size_code_units;
+  }
+  if (size_code_points == end) {
+    return std::pair{start_code_units, size_code_units};
   }
   return absl::InvalidArgumentError(
       "<string>.substring(<start>, <end>): <start> or <end> is greater than "
@@ -697,8 +700,11 @@ absl::StatusOr<std::pair<size_t, size_t>> SubstringImpl(const absl::Cord& cord,
     ++size_code_points;
     size_code_units += code_units;
   }
-  if (size_code_points == start && start == end) {
-    return std::pair{size_code_units, size_code_units};
+  if (size_code_points == start) {
+    start_code_units = size_code_units;
+  }
+  if (size_code_points == end) {
+    return std::pair{start_code_units, size_code_units};
   }
   return absl::InvalidArgumentError(
       "<string>.substring(<start>, <end>): <start> or <end> is greater than "
diff --git a/common/values/string_value_test.cc b/common/values/string_value_test.cc
index 6bfcb83aa..c64151034 100644
--- a/common/values/string_value_test.cc
+++ b/common/values/string_value_test.cc
@@ -475,6 +475,12 @@ TEST_F(StringValueTest, Substring) {
   EXPECT_THAT(unicode_view.Substring(1, 2, arena()), StringValueIs("€"));
   EXPECT_THAT(unicode_cord.Substring(2, 4, arena()), StringValueIs("€€"));
   EXPECT_THAT(unicode_view.Substring(2, 4, arena()), StringValueIs("€€"));
+  EXPECT_THAT(unicode_cord.Substring(4, 6, arena()), StringValueIs("€€"));
+  EXPECT_THAT(unicode_view.Substring(4, 6, arena()), StringValueIs("€€"));
+  EXPECT_THAT(unicode_cord.Substring(0, 6, arena()), StringValueIs("€€€€€€"));
+  EXPECT_THAT(unicode_view.Substring(0, 6, arena()), StringValueIs("€€€€€€"));
+  EXPECT_THAT(unicode_cord.Substring(6, 6, arena()), StringValueIs(""));
+  EXPECT_THAT(unicode_view.Substring(6, 6, arena()), StringValueIs(""));
   EXPECT_THAT(unicode_cord.Substring(2, arena()), StringValueIs("€€€€"));
   EXPECT_THAT(unicode_view.Substring(2, arena()), StringValueIs("€€€€"));
 
diff --git a/extensions/strings_test.cc b/extensions/strings_test.cc
index c3059808f..46d9908eb 100644
--- a/extensions/strings_test.cc
+++ b/extensions/strings_test.cc
@@ -221,7 +221,10 @@ INSTANTIATE_TEST_SUITE_P(
         "'tacocat'.substring(4) == 'cat'", "'tacocat'.substring(7) == ''",
         "'tacocat'.substring(0, 4) == 'taco'",
         "'tacocat'.substring(4, 4) == ''",
+        "'tacocat'.substring(4, 7) == 'cat'",
+        "'tacocat'.substring(0, 7) == 'tacocat'",
         "'ta©o©αT'.substring(2, 6) == '©o©α'",
+        "'ta©o©αT'.substring(4, 7) == '©αT'",
         "'ta©o©αT'.substring(7, 7) == ''",
 
         // Tests for reverse()